The present invention relates to a vehicle suspension mounting structure arranged in a portion where a suspension device for suspending a vehicle body is mounted.
As a suspension device for a vehicle, for example, a so-called double-wishbone suspension device for supporting a vehicle wheel by A-shaped upper and lower arms is known, as disclosed in Japanese Utility Model Laid-Open No. 62-187904. In the double-wishbone suspension device, the position of a vehicle wheel is basically regulated by the upper and lower arms. For this reason, the relationships among the positions, arrangements, and lengths of these arms are selected to minimize squat upon starting of a vehicle or a change in camber angle or scuff when a vehicle wheel is moved in the vertical direction with respect to a vehicle body.
During travel of a vehicle, a shock load in the back-and-forth direction is input to a vehicle wheel due to a rough road surface. In the double-wishbone suspension device, since the upper arm (also the lower arm) is pivotally supported at two points, i.e., front and rear points, a rigidity in the direction of the shock load is increased. As a result, the shock is transmitted to the vehicle body, thus impairing riding comfort.
In order to eliminate the drawback of the riding comfort of the double-wishbone suspension device, elastic bushings in the two supporting portions of each arm are softened to decrease a support rigidity of a vehicle wheel in the back-and-forth direction. When the support rigidity is decreased, however, a support rigidity about a rotating shaft of a vehicle wheel is also decreased. As a result, the natural frequency of the support mechanism is decreased, and this causes resonation with a vibration of, e.g., a disk in a brake device provided to the vehicle wheel. In this manner, a so-called "brake jadder" undesirably occurs.
More specifically, in the double-wishbone suspension device having a normal structure, as disclosed in Japanese Utility Model Laid-Open No. 62-187904, riding comfort or brake jadder must be sacrificed, or both must be sacrificed to some extent.
To solve this problem, another structure is proposed. For example, as disclosed in Japanese Utility Model Publication No. 62-1762, a vehicle wheel support member is extended upward from a rim of a vehicle wheel, and an upper arm is mounted on the extended portion, so that a distance between the mounting point and the rotating shaft of the vehicle wheel is increased (a so-called high-mount double-wishbone suspension device). With this structure, the brake jadder can be prevented by a small force, and softer elastic bushings provided at two support points of the upper arm to the vehicle body can be used, thereby achieving both an improvement in riding comfort and prevention of brake jadder.
As described above, the so-called high-mount double-wishbone suspension device can achieve both improvement in riding comfort and prevention of brake jadder. However, another problem is posed.
More specifically, the upper arm of the double-wishbone suspension device comprises an A-shaped arm whose support points to a vehicle body are two points separated in the back-and-forth direction. In this manner, in order to allow the upper arm to swing in correspondence with vertical movement of a vehicle wheel, a wide space is required. However, it is difficult to assure a sufficient space since various parts must be arranged above the rim inside the vehicle wheel. For this reason, as shown in the drawing of the Japanese Utility Model Publication No. 62-1762, the length of the upper arm is decreased, and the upper arm must be obliquely arranged. When the length of the upper arm is decreased, a change in camber angle becomes too large upon vertical stroke of the vehicle wheel.
In order to eliminate the above drawbacks, the present applicant filed "Vehicle Suspension Device" as Japanese Patent Application Laid Open No. 1-4873 on Jan. 13, 1990. According to this prior art, in a vehicle suspension device which swingably supports, via upper and lower arms, a vehicle wheel support member for rotatably supporting a vehicle wheel with respect to a vehicle body, at least the upper arm is constituted by two link members disposed to be spaced apart by a predetermined distance in the vertical direction of the vehicle body with respect to the vehicle wheel support member, so that a displacement of the vehicle wheel support member in the back and forth direction of the vehicle body is mainly regulated by the upper link member, and a displacement of the vehicle wheel support member in the widthwise direction of the vehicle body is mainly regulated by the lower link member.
According to the vehicle suspension device disclosed in this prior art, both improvement in riding comfort and prevention of brake jadder can be achieved, and the change in camber angle can have a desired tendency.
However, in this suspension device, since a very large load acts on a mounting portion of the upper one of the two link members constituting the upper arm, if a mounting rigidity of this portion is low, a vibration which makes a driver and passengers uncomfortable is generated at the mounting portion.